The present invention relates to a method for the preparation of a semiconductor device by untrafine working. In particular, the present invention is directed to a method characterized by the ultrafine working of a semiconductor device, by pattern-wise etching of a metal layer to form a patterned layer or wiring of the metal on the substrate surface.
Wiring and electrodes or semiconductor devices are usually formed by aluminum, which is highly electroconductive metal suitable therefor. The pattern-wise layer of a metal on the substrate surface for the wiring and the like is conventionally formed by a method, comprising the steps of (1) vacuum depositing or sputtering a metal layer on the substrate surface having an electrically insulating film thereon, (2) forming a pattern-wise layer of a resist material on the metal layer, which is susceptible to light or actinic rays, such as electron beams, (3) etching of the unprotected surface of the metal with an etching solution containing, for example, phosphoric acid of an amine in the so-called wet process, and finally, (4) removing the film of the resist, thereby leaving the pattern-wise layer of the metal, e.g. aluminum, for the wiring and the like.
In recent years, the technology of electronics has been under rapid growth toward higher degrees of integration and increased performance of the semiconductor devices. This is represented by the transition from LSIs to ultra-LSIs. Thus, the requirements for finer working of semiconductor devices are escalating. A fineness of about 3 micrometers can be achieved by the conventional wet process of etching an aluminum surface for the preparation of a miniaturized semiconductor device. A further fineness of 2.5 to 2 micrometers or in the so-called submicron range of 1 micrometer or finer, can be achieved only by using the so-called dry etching method in place of the conventional wet process, from the standpoints of the dimensional accuracy and uniformity of etching, increasing requirements for an improved cross-sectional forms of the etched pattern, and higher yield of the products.
While dry etching of an aluminum film can be performed in principle by use of a chlorine-containing gas, practical and feasible methods for the dry etching of aluminum film include the so-called reactive ion etching (RIE) method and plasma etching methods, the latter of which uses a pair of parallel plate electrodes. These methods are capable of exhibiting a mechanical force on the aluminum surface, which is readily covered with a surface film of aluminum oxide and barely susceptible to etching by the chemical means alone. When the above mentioned RIE method or plasma etching is used on an aluminum film, the temperature of the surface is remarkably increased, due to the energetic conditions of etching or bombardment of the surface with strongly accelerated ions. As a consequence, thermal deformation is sometimes unavoidable when the resist masking is made of a conventional organic resist material, which are susceptible to actinic rays such as ultraviolet light, electron beams, X-rays. This results in a decreased resolving power of the etched pattern by decreasing the distance between the patterned lines. Alternatively, an unusually large decrease in the film thickness of the resist layer may result. Thus, no satisfactory organic material is available suitable for use as a resist masking, which is capable of withstanding the severe conditions encountered in the dry etching of an aluminum film on the substrate surface.
A procedure for compensating for the decrease in the thickness of the resist film may be to increase the thickness of the resist film, thereby taking into account the decrease in thickness during processing. However, this method is not always applicable, because it results in a decrease of accuracy or resolving power when patterning the resist layer, due to the increased thickness thereof.